1. Field of the Invention
The present invention relates to an image-forming medium, coated with a layer of microcapsules filled with dye, on which an image is formed by selectively squashing and breaking the microcapsules in the layer of microcapsules.
2. Description of the Related Art
Conventionally, an image-forming medium, coated with a layer of microcapsules filled with different color dyes or inks, is known. The respective different color dyes or inks are transparent at a normal ambient temperature, but each ink develops a monochromatic color at a specific temperature. Thus, the respective different colors are selectively developed on the microcapsule layer by selectively applying specific temperatures to the microcapsule layer. In this case, it is necessary to fix a developed color by irradiation, using a light of a specific wavelength. Accordingly, this color-image-forming system is costly, because an additional irradiation apparatus for the fixing of a developed color is needed, and electric power consumption is increased due to the additional irradiation apparatus. Also, since a heating process for the color development and an irradiation process for the fixing of a developed color must be carried out with respect to each color, this hinders a quick formation of a color image on the color-image-forming medium.
Further, conventionally, a surface of the microcapsule layer is frequently covered with a transparent film sheet such that the microcapsules included therein are protected from being scratched. Also, because of the existence of the transparent film sheet, it is possible to vividly and sharply observe a color image formed on the microcapsule layer. Note, as well known, for example, a color image drawn on a sheet of paper can be more vividly and sharply observed through the intermediary of a transparent layer closely covering the drawn color image, in comparison with a case where the drawn color image is directly observed. Nevertheless, the transparent film sheet may be thermally shrunk due to the application of the heating temperature. Of course, when the transparent film sheet is subjected to the thermal shrinkage, the color image, formed on the microcapsule layer, may be distorted due to the shrinkage of the transparent film sheet. Although the thermal shrinkage of the transparent film sheet can be prevented by increasing a thickness of the transparent film sheet, it is impossible to make the thickness of the transparent film sheet thicker, because the application of the heating temperature to the microcapsules is hindered by the thickened transparent film sheet.
Therefore, an object of the present invention is to provide an image-forming medium coated with a layer of microcapsules filled with ink associated with an image-formation layer, in which an image can be quickly formed on the image-formation layer at a low cost by selectively squashing and breaking the microcapsules under predetermined temperature/pressure conditions.
Another object of the present invention is to provide an image-forming medium as mentioned above, in which the image-formation layer is closely covered with a sheet of transparent film sheet such that the transparent film sheet cannot be subjected to any thermal shrinkage when the microcapsules are selectively squashed and broken under the predetermined temperature/pressure conditions.
In accordance with a first aspect of the present invention, there is provided an image-forming medium comprising a transparent base member, an image-formation layer coated over the transparent base member, and a layer of microcapsules, coated over the image-formation layer. In this case, an image is formed as a mirror image on the microcapsule layer by the discharged first single-color ink, and is observed through the intermediary of the transparent film sheet.
In accordance with a second aspect of the present invention, there is provided an image-forming medium comprising a base member, a layer of microcapsules coated over the base member, and an image-formation layer coated over the microcapsule layer. In this case, an image is formed as a mirror image on the microcapsule layer by the discharged first single-color ink, and is observed from a side of the image-formation layer opposed to the microcapsule layer.
In any event, according to the present invention, the microcapsule layer contains a first type of microcapsule, filled with a first single-color ink, which exhibits a first temperature/pressure characteristic such that each microcapsule is squashed under a first predetermined pressure at a first predetermined temperature, whereby the first single-color ink is discharged from the squashed microcapsule. The image-formation layer is constituted such that the discharged first single-color ink is developed in the image-formation layer.
The microcapsule layer may further contain a second type of microcapsule, filled with a second single-color ink, which exhibits a second temperature/pressure characteristic such that each microcapsule is squashed under a second predetermined pressure at a second predetermined temperature, whereby the second single-color ink is discharged from the squashed microcapsule, the discharged second single-color ink being developed in the image-formation layer.
Furthermore, the microcapsule layer may contain a third type of microcapsule, filled with a third single-color ink, which exhibits a third temperature/pressure characteristic such that each microcapsule is squashed under a third predetermined pressure at a third predetermined temperature, whereby the third single-color ink is discharged from the squashed microcapsule, the discharged third single-color ink being developed in the image-formation layer.
Preferably, the first, second and third single-color inks form three primary colors, such as cyan, magenta and yellow.
The image-formation layer may be formed as a porous layer comprising white powder, and the development of the discharged first single-color ink in the image-formation layer is carried out by permeation of the discharged first single-color ink into the porous layer. Preferably, the white powder is selected from the group consisting of calcium carbonate powder, titanium dioxide powder, silica powder and white clay powder.
The image-formation layer may have a thickness of about 0.02 mm to about 0.1 mm. In the first aspect of the present invention, the transparent base member may be formed as a sheet of transparent synthetic resin film having a thickness of about 0.2 mm. Preferably, the transparent synthetic resin film sheet is formed of polyethylene terephthalate.
In the first aspect of the present invention, the image-forming medium may further comprises a sheet of protective synthetic resin film covering the microcapsule layer and having a thickness thinner than that of the transparent synthetic resin film sheet. Also, in the second aspect of the present invention, the base member may be formed as a sheet of protective synthetic resin film covering the microcapsule layer.
The protective synthetic resin film sheet may be formed of polyethylene terephthalate, and has a thickness of about 0.025 mm. Preferably, the protective synthetic resin film sheet is colored white. Further, the protective synthetic resin film sheet may be formed as a metallized film sheet.
Each of the first, second and third single-color inks may be composed of a leuco-pigment. In this case, the image-formation layer contains a color developer, with which a discharged single-color ink is chemically reacted to develop a given single color in the image-formation layer. Optionally, the image-formation layer may be formed as a solid color developer layer, with which a discharged single-color ink is chemically reacted to develop a given single-color in the image-formation layer.